1. Field of the Invention
The present invention relates to an in plane switching mode liquid crystal display device, and particularly, to an in plane switching mode liquid crystal display device and fabrication method of improving an aperture ratio.
2. Description of the Related Art
Liquid crystal display devices have been typically used because they consume low power and provide a high picture quality. A liquid crystal display device is formed by attaching a thin film transistor array substrate and a color filter substrate face to face with a uniform interval therebetween, and placing a liquid crystal layer between the thin film transistor array substrate and the color filter substrate.
Pixels are arranged on the thin film transistor array substrate in a matrix. A thin film transistor, a pixel electrode and a capacitor are formed within a pixel. A common electrode, an RGB color filter and a black matrix are formed on the color filter substrate. The common electrode applies an electric field to the liquid crystal layer together with the pixel electrode. The RGB color filter provides color display capabilities. An alignment film is formed at facing surfaces of the thin film transistor array substrate and the color filter substrate and is rubbed to orient the liquid crystal layer in a specified direction.
When an electric field is applied between the pixel electrode and the common electrodes, the liquid crystal rotates due to a dielectric anisotropy. As a result, light is transmitted or blocked by pixels to display a character or an image. However, such a twisted nematic mode liquid crystal display device has a narrow viewing angle. In-plane switching mode LCD arrangements have been introduced to improve the narrow viewing angle by aligning liquid crystal molecules in a substantially horizontal direction with respect to the substrate.
FIG. 1A depicts a plan view of an in-plane switching mode liquid crystal display (LCD) device in accordance with a related art arrangement. FIG. 1B illustrates a sectional view of an in-plane switching mode liquid crystal display (LCD) device in accordance with a related art arrangement. As shown in FIG. 1A, gate lines 1 and data lines 3 are arranged horizontally and vertically, respectively, on a first transparent substrate 10, defining pixel regions. Although in an actual liquid crystal display device, the ‘N’ number of gate lines 1 and the ‘M’ number of data lines 3 cross each other to create an N×M number of pixels. Only one pixel is shown in FIG. 1A for explanatory purposes.
A thin film transistor 9 is disposed at a crossing of the gate line 1 and the data line 3. The thin film transistor 9 includes a gate electrode 1a, a semiconductor layer 5 and source/drain electrodes 2a and 2b. The gate electrode 1a is connected to the gate line 1. The source/drain electrodes 2a and 2b are connected to the data line 3. A gate insulation layer 8 is formed on the entire substrate.
A common line 4 is arranged parallel to the gate line 1 in the pixel region. A pair of electrodes, which are a common electrode 6 and a pixel electrode 7, are arranged parallel to the data line 3 for switching liquid crystal molecules. The common electrode 6 is simultaneously formed with the gate line 1 and connected to the common line 4. The pixel electrode 7 is simultaneously formed with the source/drain electrodes 2a and 2b and connected to the drain electrode 2b of the thin film transistor 9. A passivation film 11 is formed on the entire surface of the substrate 10 including the source/drain electrodes 2a and 2b. A pixel electrode line 14 is formed to overlap the common line 4 and is connected to the pixel electrode 7. The pixel electrode line 14, the common line 4, and the gate insulation layer 8 interposed therebetween, form a storage capacitor (Cst).
A black matrix 21 and a color filter 23 are formed on a second substrate 20, on which an overcoat film is formed for flattening the color filter 23. The black matrix 21 prevents light leakage to the thin film transistor 9, the gate line 1 and the data line 3. The color filter 23 provides color display capabilities to the liquid crystal display device. Alignment films 12a and 12b are formed at facing surfaces of the first and second substrates 10 and 20. The alignment films 12a and 12b determine an initial alignment direction of the liquid crystal. A liquid crystal layer 13 is formed between the first and second substrates 10 and 20. The light transmittance of the liquid crystal layer 13 is controlled by a voltage applied between the common electrode 6 and the pixel electrode 7.
The in-plane switching mode LCD device having such a structure as described above with respect to the related art can advantageously improve a viewing angle because the common electrode 6a and 6b and the pixel electrode 7 are disposed on the same plane.
However, the in-plane switching mode LCD device is disadvantageous in that an aperture ratio is degraded because the common electrode 6 and the pixel electrode 7 are disposed in a pixel region where an image is displayed, which results in deterioration of brightness.
In addition, a lateral electric field is not normally formed in the pixel because of signal interference between the data line 3 and the pixel electrode 7. In order to solve such signal interference, a common line 6b is disposed at a region adjacent to the data line 3. The common electrode 6 disposed at an outer edge of the pixel acts as a shielding line for shielding a data signal and is formed to be wider than the common electrode 6 positioned at a central portion of the pixel, thereby reducing the aperture ratio.